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II
438 MINING STATISTICS WEST OF THE ROCKY MOUNTAINS.
added, and the whole is quickly heated to a cherry red. In this stag®
oí the process the oxide of lead is reduced and the sulphuric acid
partly driven off as sulphurous acid by the action of the coal, all f
partly expelled by the silica, which takes its place, forming
lead. After the ebullition of the charge has ceased, about 1
silicate o/
ar CCH''
10 per
ol metallic iron is added and another heat is given, by which the lea 1 1
oof YV.,v,. „ ; • . .Li 1 ® 1. J -r,. L.1 „ „,.os SUD'
set free, while the iron goes into the slag as a silicate. If the ores
jected to this treatment contain silver, very little of this will pass
sab-
into
— ^ wvufvmvuu IA/HUUU Ol lVWj lit LI Ü VI LI I IfO n 111 |1y
the slag when the process is properly managed, because there are V 10 ^] I
oxides present ; but there is always a considerable loss of lead in to
slag. It is of course very important in this method to get the correct P 1
portions of silica and iron, which are to be added. As we cannot ha»
the process entirely in our power, this is always difficult. , ¿
This process is on account of the quick returns which it gives, adapt®
for use in this country, for smelting silver ores in localities where n‘° >
iron ores, or basic iron slags can be had at a small cost. The pr° ce .u
executed in Newark, New Jersey, is identical with it in principle, then 1 »
it differs slightly in some details. For use in the West, however, ‘
1 il O of ■ftiimnnrv -Z a * l * 11 1 • i • j _ ..n/loV'
blast-furnace process is far superior to it in
velopment
all districts now under
III. SMELTING IN BLAST FURNACES.
The blast furnace is the best adapted for the smelting of the ri®
argentiferous lead ores, or of mixtures of lead ores with silver ores in 0
western mining districts. These ores carry usually considerable Q u ‘ l ¿
titles ol earthy matter and silica, besides the various combinations
metals other than lead and silver. For this reason alone they arc 11
well suited for any of the reverberatory processes. But in addition
blast-furnace process requires less fuel and labor in proportion to
yield. It is true, the volatilization of lead is somewhat greater in ,
blast-furnace than in the reverberatory ; but this may be partly a vol( fc
by a proper shape and height of the furnace ; and by far the hu'g,
percentage oí the volatilized lead and silver may be caught in prope*
constructed systems of condensing chambers, especially when sho" r
oí water are used to cool the fumes. M
Galena ores containing little silver, and no other metals, but m 11
earthy gangue are usually subjected to the process known as the P .
cipitation process, those containing much silver, and besides the ah j
substances a large percentage of foreign sulphurets, arson inrots,
to Iffe roasting and reducing process. In the latter, a precipité, ®
action is also often introduced either by oxides of iron already i u he
charge, or by a small addition of materials containing them. F° r
latter process, the western ores are eminently fitted. i a .
I lie furnaces used heretofore, vary greatly in shape, and their
tn e meiits have been often discussed by metallurgical writers. ^ ll i e ,
it to say, that the Hachette furnace and the Piltz furnace, (both
scribed in the remarks on Eureka District, Nevada, in a former chap 1
of this report,) are now conceded on all sides to be the best. They h a A
the largest capacity, and are the most economical in regard to fuel 1 , ^
labor, while the loss of lead in the slag is exceedingly small.
latest modification of the Piltz furnace, as introduced lately in
thal, Germany, the slag contains only ¡ per cent, of lead, while W
erly from 4 to 0 per cent, was not uncommon. The loss by volatile.',
is also greatly reduced. This is partly due to the manner of efiarg' 11 e
and partly to the shape of the furnace.
